FIG. 1 is an explanatory view of a cooling cycle used in refrigerators according to the prior art. The cooling cycle includes a compressor 1, a condenser 2, a valve 3, fans 4 and 5, evaporators 6 and 7, a controller 8, and expansion means 9 and 10. The compressor 1 compresses refrigerants into high-temperature, high-pressure gaseous refrigerants, and the condenser 2 condenses the refrigerants having passed through the compressor to high-temperature, high-pressure liquid refrigerants. The valve 3 controls a refrigerant flow into the evaporator 6 of a high-temperature section and the evaporator 7 of a low-temperature section, and a 3-way valve having one inlet and two outlets is typically used. Hereinafter, an evaporator and a fan corresponding to a storage compartment that stores objects at high temperature will be referred to as a high temperature evaporator and a high temperature fan, respectively. Similarly, an evaporator and a fan corresponding to a storage compartment that stores objects at low temperature will be referred to as a low temperature evaporator and a low temperature fan, respectively. When a refrigerant is sent to the high temperature evaporator 6, the high temperature fan 4 starts running thereby cooling an upper storage compartment. Likewise, when a refrigerant is sent to the low temperature evaporator 7, the low temperature fan 5 starts running thereby cooling a lower storage compartment. That is, the high temperature fan 4 has a role in circulating cool air generated from the high temperature evaporator 6 into the high temperature storage compartment, and the low temperature fan 5 has a role in circulating cool air generated from the low temperature evaporator 7 into the low temperature storage compartment.
FIG. 2 graphically explains a control method of a parallel-type refrigerator according to the prior art. According to the graph, from t0 to t1 and from t2 to t3, a storage compartment for storing items at high temperature and a storage compartment for storing items at low temperature do not need to be cooled, so the high temperature fan 4 and the low temperature fan 5 are not running and the compressor 1 is also deactivated. Depending on the type of refrigerator, even if a cooling operation is not required, the fans may be turned ON/OFF automatically with a preset cycle so as to maintain a uniform temperature in the storage compartments. From t1 to t2, the high temperature storage compartment needs to be cooled off so the high temperature fan 4 is activated; from t3 and t4, the low temperature storage compartment needs to be cooled off so the low temperature fan 5 is activated.
In conventional refrigerators, the low temperature evaporator is set to −25˜−29° C., and the high temperature evaporator is set to −16˜−20° C. In order to cool the high temperature storage compartment at the completion of cooling of the low temperature storage compartment (t4 in FIG. 2), refrigerants in the low temperature evaporator 7 must be taken into the compressor 1 again and eventually to the high temperature evaporator 6 via the condenser 2. However, when the fan is operated in this manner, refrigerants stay in the low temperature evaporator 7 because the low temperature fan 5 at t4 is not activated. Without the low temperature fan 5 in operation mode, an amount of heat being exchanged between the low temperature evaporator and the low temperature storage compartment is not much. This leads to an increase of temperature difference between the low temperature evaporator and the high temperature evaporator, and a pressure in the low temperature evaporator becomes much lower than a pressure in the high temperature evaporator, eventually impeding a smooth flow of refrigerants from the low temperature evaporator to the high temperature evaporator. That is to say, when cooling of the high temperature storage compartment is initiated (t5 in FIG. 2) at the end of cooling of the low temperature storage compartment, refrigerants do not move sufficiently to the high temperature evaporator 6, thereby interrupting the performance of a smooth cooling operation.